The conventional linear track rail refers to a solid sliding base endlessly moving along the rail. There is a loaded path formed between the sliding base and the rail, and the sliding base has an unloaded path. Two direction change paths are formed in two ends of the sliding base so as to be connected between the loaded path and the unloaded path. The two direction change paths, the loaded path and the unloaded path form an endless circulation path, and multiple balls are moved along the endless circulation path to achieve the purpose of the movement of the sliding base.
In order to ensure that the balls are moved along the correct path of the endless circulation path and do not hit each other. A ball retainer is used to separate each of the balls. The ball retainer is guided by the top and bottom grooves. U.S. Pat. No. 5,988,883 discloses an endless retainer wherein the groove slopes/portions of the retainer of the loaded path and the unloaded path are parallel such that the two portions of the retainer can smoothly pass through the direction change paths. Besides, the balls of the loaded path have contact faces contacting the rail to support the force between the sliding base and the rail. In order to obtain a larger contact face for each ball, the retainer is parallel to the tangential face of the contact face, or the retainer is inclined by a small angle relative to the tangential face of the contact face to avoid interfere between the retainer and the rail. However, the above-mentioned arrangement generates an angle between the endless circulation path and the horizontal plane, and increases the height of the sliding base.
Furthermore, the linear rail is developed to be smaller than before so that the angle between the endless circulation path and the horizontal plane has to be reduced. U.S. Patent Publication No. 20070147714 discloses that the sliding base has two endless circulation paths on each of two sides thereof and a smaller angle is formed between each endless circulation path and the horizontal plane so as to obtain a smaller sliding base. However, the above-mentioned arrangement makes one end of the retainer to be too close to the rail and the retainer may drop and hit the rail.
The present invention intends to provide an endless circulation path for a linear rail and improves the shortcomings of the conventional endless circulation path.